KiCad

KiCad is a free and open source EDA (electronic design automation) software for editing circuit schematics, PCB layouts and component libraries, with Gerber and drill output.

Features
First released in 1992, KiCad is considered mature and is used for the successful development and maintenance of complex electronic boards. It doesn't impose limitations such as board size or number of pins, etc. and can handle multiple layers. Being open source it's an ideal tool for Open-source hardware projects. KiCad is available for Linux, Windows and Apple OS X (experimental, but working).

Quick start hints
To help get quickly familiar with KiCad's user interface (UI).
 * Entering a ? pops up a list of hot keys. Using these is more efficient than relying on the mouse alone.
 * Open-source software is not as polished as proprietary. If the program behaves strangely, check for known bugs.

KiCad project manager
KiCad is the project manager window. This gives access to eight stand-alone software tools: Eeschema, Schematic Library Editor, Pcbnew, PCB Footprint Editor, GerbView, Bitmap2Component, PCB Calculator and Pl Editor.

Eeschema
Eeschema is the schematic editor and component editor window.

CvPcb
CvPcb the footprint selector helper is always run from Eeschema.

Check every component and footprint before use, to ensure that they match the features required.

Pcbnew
Pcbnew is the circuit board layout editor and footprint editor.

Other tools
Other tools in KiCad include GerbView a Gerber and drill viewer, Bitmap2Component, PCB Calculator and Pl Editor.

Version control
All version control systems (VCS), such as Git can handle text and binary files but binary ones cannot be merged. KiCAD files are plain text.

Further libraries
Check component pin-outs, silk screens, etc. are correct before sending for manufacture.
 * KiCad component libraries with footprints, CC-BY-SA or GPL licenced
 * KiCad libraries
 * Kicad libraries converted from Eagle

Utilities

 * Quick IC symbol builder
 * KiCad Librarian
 * KiPart, generates schematic part libraries from CSV files.
 * Special techniques for Kicad by Robin Whittle, Apr. 2016

KiCad format SDIY files
Some useful examples, not a comprehensive list.
 * SMRL Vactrol Sequencer
 * KiCad Synth DIY Synthblocks

Annoyances

 * One annoyance of KiCAD solved - F4 Drag, EEVblog forum, March 2012
 * All the ways KiCad annoys me, Head-Fi.org forums, Feb. 2015
 * I want to love KiCad, Reddit, Jan. 2016